Introduction: Perinatal thyroid hormone deficiency causes irreversible damage to auditory system functions in rats 1). Hearing loss has potential to affect communication behavior. We used rats as an animal model because they emit ultrasonic vocalizations (USVs) interacting with others. We examined whether perinatal thyroid hormone deficiency affects USV emissions.

Methods: Pregnant rats were treated with the antithyroid drug methimazole (MMI) from gestational day 15 to postnatal day (PND) 21 via drinking water. The concentrations of MMI (w/v) were 0% (control), 0.01% (low dose), and 0.015% (high dose). The USVs in the neonatal rats were recorded for 5 min of maternal separation on PND 5, 10, 15, and 20. On PND 42-43, three juvenile rats of the same sex and same MMI dose but from the different litter were grouped and their USV emissions were recorded for 30 min.

Results: The MMI-treated neonatal rats produced more USVs than the control rats when they were separated from mother rats. The high-dose juvenile rats increased USV emissions compared with the control rats when they were staying together.

Discussion: Neonatal rats emit 40-50 kHz USVs on separation from mother rats 2). Juvenile rats emit 20-30 kHz USVs playing together 3). In this study, the MMI-treated rats produced more USVs than the control. They were not able to hear USVs emitted by themselves and others due to hearing loss. We conclude that perinatal thyroid hormone deficiency has potential to affect communication behavior maintained through USV emissions.